Previously, an organic EL device as shown by a reference numeral 201 in FIG. 9 is known as such a kind of organic EL device.
In this organic EL device 201, a wiring layer 203, a hole injection layer 204, a hole transporting layer 208, a luminescent layer 209, an electron transporting layer 210, an electron injection layer 206, and an electrode layer 207 are formed on a surface of a substrate 202 in this order.
A first organic layer 205 is constituted by the hole transporting layer 208, the luminescent layer 209 and the electron transporting layer 210.
A side of the first organic layer 205 that contacts the electron injection layer 206 is the electron transporting layer 210, which is a thin film composed mainly of an organic material having electron transportability.
The electron injection layer 206 is a thin film composed of a metallic material having electron injectability; and for example, a single material or a chemical compound of an alkali metal element (such as, lithium or an alkaline earth metal element) is used.
In this organic EL device 201, the electron injection layer 206 is formed on a surface of the first organic layer 205 by a vapor deposition method, and the electrode layer 207 is formed on a surface of the electron injection layer 206 by the vapor deposition method.
In the vapor deposition method for the electrode layer 207, problems (such as, a deformation of a mask) occur due to a heat load during the film formation, which make larger substrates difficult. Therefore, the formation of the electrode layer 207 by a sputtering method has been tried.
However, it is known that when the electrode layer 207 is formed by the sputtering method, the luminescent efficiency is deteriorated. Thus, a solution has been sought.
Meanwhile, in an organic EL device 301 of FIG. 15, a wiring layer 303, a first luminescent part 320, an electrode layer 311, a second luminescent part 321 and an electrode layer 304 are formed on the substrate 302.
First and second luminescent parts 320, 321 comprise first and second organic layers 305, 306, first and second hole injection layers 307, 308 being disposed on those surfaces of the first and second organic layers 305, 306 which are at sides of the substrate 302, respectively; and first and second electron injection layers 309, 310 are disposed on surfaces at the opposite sides.
The electrode layer 311 separates the first electrode injection layer 309 and the second hole injection layer 308 having different polarities from each other, and the first electron injection layer 309 and the second hole injection layer 308 are electrically connected.
When a voltage is applied between the wiring layer 303 and the electrode layer 304, voltages are applied between the first hole injection layer 307 contacting the wiring layer 303 and the first electron injection layer 309 connected to the electrode layer 311 and between the second electron injection layer 310 contacting the electrode layer 304 and the second hole injection layer 308 connected to the electrode layer 311, so that holes are injected from the first and second hole injection layers 307, 308 into the first and second organic layers 305, 306 and electrons are injected from the first and second electron injection layers 309, 310 into the first and second organic layers 305, 306. The injected holes and the electrons are recombined with each other inside the first and second organic layers 305, 306, respectively, thereby generating light.
In this embodiment, the substrate 302 is transparent; the wiring layer 303 and the second organic layer 306 on the substrate 302, and each of the layers 307, 305, 309, 311 and 308 therebetween are transparent. Thus, the light radiated in the first organic layer 305 is emitted from the first organic layer 305 to the outside of the substrate 302 through the first hole injection layer 307 and the wiring layer 303. The light radiated in the second organic layer 306 is emitted from the second organic layer 306 to the outside of the substrate 302 through each of the layers 308, 311, 309, 305 and 307 among the substrate 302 and the second organic layer 306. The light from the second organic layer 306 is emitted toward the same side as in the case of the light from the first organic layer 305, so that an emitted strong light in which both the lights are combined is observed at a place on the side of the substrate 302 outside the organic EL device 301.
There is a sputtering method as a method for forming a thin film composed of a metal (such as, the electrode layer 311) on the surface of the first electron injection layer 309.
The first electron injection layer 309 is a thin film of a metallic compound having the electron injectability; and the first organic layer 305 is constituted by a thin film of an organic compound. It is known that when the electrode layer 311 of a metal is formed on a surface of the first electron injection layer 309 as the thin film of the organic compound by sputtering a metallic target, the luminescent efficiency decreases more as compared to the film formation by the vapor deposition method.
For this reason, the vapor deposition method is used in forming the electrode layer 311 on the surface of the first electron injection layer 309.
However, since the vapor deposition method has problems (such as, a slow film forming speed), a technology has been sought, which can form the electrode layer 311 by the sputtering method, while the luminescent efficiency equivalent to that in the vapor deposition method is maintained. See, Nos. JP-A 2004-79538, JP-A 2006-302506, JP-A 2005-26003, and 2004-164992.